Based on high-resolution channel structures and functional mutagenesis, we have identified a physical site for alcohol-mediated activation of GIRK channels. Amino acid substitutions that increased the molecular side-chain volume at a conserved Leu in the βD-βE ribbon of the hydrophobic pocket of GIRK2 decreased alcohol-mediated activation of GIRK channels (see Fig. 8a). In particular, two substitutions, Trp and Tyr, at the Leu in the hydrophobic pocket of GIRK2 (L257) and GIRK4* (L252) channels produced a progressive loss in alcohol activation. For GIRK4*, Ala substitution increased the amplitude of alcohol-activated currents. Thus, increasing or decreasing the volume of the pocket by altering the amino acid side-chain produced changes in alcohol activation. Similarly, the size of the putative alcohol-binding pocket in GABAA α1 and glycine receptors is important for determining modulation by alcohol and other small anesthetics. Increasing the bulkiness of amino acids in the putative alcohol-binding pocket of these channels eliminates the modulation by EtOH3 or isofluorane30. By contrast, decreasing the size of amino acids in the same region of the decanol-insensitive GABA ρ1 receptors now enables potentiation by decanol3,6. Taken
